Process for the isomerization of allo-ocimene



Patented Sept. 16, 1941 PROCESS FOR THE ISOMERIZATION OF ALLO-OCMENE Leo A. Goldblatt, New Orleans, La., assignor to United States of America, as represented by the Secretary of A riculture No Drawing. Application March 23, 1945, Serial No. 584,485

4 Claims.

(Granted under the act of March 8, 1883, as amended April 30, 1928; 370 0. G. 757) 1 V This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described and claimed, if patented, may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment to me of any royalty thereon.

This invention relates to terpenes and is more particularly concerned with the treatment of allo-ocimene for the purpose of producing other terpenes.

Allo-ocimene, also known as 2,6-dimethyl-2,4,6- octatriene, is an acyclic terpene hydrocarbon having the structural formula:

Allo-ocimene may be obtained in good yield by the non-catalytic vapor phase thermal isomerization of the bicyclic terpene a-pinene in accordance with the procedure disclosed in copending application Serial No. 352,112, filed August 10, 1940.

Both isomers and polymers of allo-ocimene may be obtained simultaneously by heating allo-ocimene in the liquid state at a temperature in the range of about 100 to 200 C., as during purification by fractional distillation. Either atmospheric or sub-atmospheric pressures may be employed as desired. The amount and proportion of the isomers and polymers that will be produced depend upon the temperature and period of heating. For example, by fractionally distilling alloocimene slowly at a pressure of 20 mm. (still pot temperature 110 C.) over a period of 200 hours, polymeric and isomeric terpenes are formed in the ratio of about 7 ,5 to 1, respectively. The isomers formed are chiefly monocyclic terpenes, boiling in the range of 48 to 72 C. at a pressure of 20 mm... and consist mainly of aand p-pyronene. The polymer is chiefly the dimer of allo-ocimene (CzoHsa), having a boiling point of approximately 180 C. at 8 mm. pressure.

By increasing the temperature and decreasing the period of heating, there is efiected an increase in isomerization and a decrease in polymerization. For example, at 400 C., the product obtained is substantially all isomeric monocyclic terpenes and only negligible quantities of the polymer are formed.

The extent of isomerization can be followed during the reaction by observing changes in refractive index or density, or both. Since allo-ocimene at 20 C. has a refractive index of 1.544

2 and a density of 0.808 gram per cc. and since the isomers have an average refractive index of about 1.475 and a density of about 0.838, while the polymer under the same conditions has a refractive index of 1.523 and a density of 0.886 gram per cc., a maidmum lowering of refractive index accompanied by a minimum increase in density will indicate the maximum proportion of isomerization and the minimum proportion of polymerization.

The extent of polymerization depends upon the temperature and time of contact. The required time of contact decreases as the temperature increases. At temperatures below about 300 C., the isomerization is very slow and is accompanied by the simultaneous formation of excess polymer. At temperatures above about 500 C., considerable decomposition occurs which is accompanied by the formation of non-condensable gas. The preferred temperature range for the isomerization is about 300 C. to 500 C. with a time of contact of about 60 to 0.1 seconds.

Maximum conversion appears to result at 440 0., using a time of contact of 7 seconds, giving a product having n =1.478 and d4 =0.836. Fractional distillation at 20 mm. shows the product obtained under these conditions to contain 00 percent of isomeric terpenes, 3 percent polymer, and 7 percent unchanged allo-ocimene. The isomeric terpenes consist chiefly of the monocycle aand fi-pyronenes in the proportion of approximately 1 to 2, respectively, having the following structural formulae, respectively:

0 H3 0 H; CE: I

H H CH; H

OH H CH: H C Ha CH3 H H H a-pyronene fi-pyronene These pyronenes are tetramethylated cyclic hydrocarbons possessing conjugated double bonds, and the carbon skeleton corresponds to the ionone type perfumes and to certain vitamins, especially Vitamin A. These compounds, therefore, are valuable as intermediates in the syn-v thesis of perfumes and vitamins, Furthermore, the conjugated double bond permits formation of the Diels-Alder type condensation products with, for example, maleic anhydride, acrolein, acrylonitrile, crotonic aldehyde, P-benzoquinone, c:- naphthoquinone, and other dienophiles, in the production of synthetic resins, plastics, esters, and so forth.

meric and polymeric terpenes are formed, and

thence separating the polymeric and isomeric terpenes from each other.

3. The process comprising heating the vapor or alio-ocimene at a temperature in the range of 300 to 500 C. for 60 to 0.1 seconds, whereby a mixture or isomeric and polymeric terpenes is formed, and thence separating and recovering the isomeric tei'penes from the reaction mixture.

4. The method comprising heating the vapor oi" allo-ocimene at a temperature or about 440 4 C. for about 7 seconds, whereby isomeric terpenes are formed, and thence separating the isomeric terpenes from the reaction mass.

-LEO A. GOLDBIA'IT.

REFERENCES CITED The following references are of record in the 0 fl'ie of this patent:

UNITED BTA'I'EiB PATENTS Name Date Rummelsburg Feb. 14, 1944 OTHER REFERENCES Goldblatt et aL, J. A. C. 8., 66. Pa es 655-6 (1944).

Arbusow, Beri hte, vol. 67, pages 563-9 (1934).

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